The placement of tubular prosthesis in various vessels is desirable in the treatment of a number of medical conditions. For example, where a vessel or a passage is obstructed it may be desirable to insert a prosthetic tube within the vessel to maintain the passage in an open condition. Such a technique may be indicated in various conditions such as where the vessel is constricted by a tumor in a manner which tends to restrict or block the flow of fluid through the vessel thus disrupting proper functioning of the vessel. One such condition is constriction or stenosis of the bile duct which may result from a tumor surrounding the duct. It is difficult to correct such a condition surgically and often the condition may not be correctable by resection. Because constriction of the bile duct causes various difficulties such as jaundice and numerous other difficulties. An external drain provides a continuous risk for infection because it presents a path for bacteria to enter the body. Additionally, there is always the risk that the tube may be inadvertently pulled out. Moreover, external drainage prevents essential bile salts from entering the digestive tract. In order to replace the bile salts it is a common procedure to have the patient drink the bile liquid collected through the drainage tube. It is essential that the condition be alleviated promptly. Often this is achieved by inserting a drainage tube percutaneously and into the bile tree of the patient's liver to permit bile to drain.
Another technique is to insert a prostethic tube into the bile duct to maintain the flow passage open through the bile duct. This technique often is preferred because it avoids complicated surgery and can be completed in a relatively short period of time. It is preferred to the drainage tube approach because continued use of a drainage tube increases the risk of infection. Prosthetic tubes may be placed in the bile duct by a number of techniques which involve insertion of catheters, probes and various devices to guide, manipulate and position the prosthesis.
One such technique is described by G. Mendez, Jr., et al percutaneous brush biopsy and internal drainage of biliary tree through endoprosthesis American Roentgen Ray Society April 1980, Pages 653-659. Mendez describes the percutaneous transhepatic placement of a tubular prosthesis which is flared at its proximal end and tapered at its distal end. The procedure involves insertion of a needle through the patient's skin and through the patient's liver to puncture a branch of the biliary tree. A guide wire then is inserted through the needle and is advanced into and through the biliary tree. The needle is removed and a catheter then is passed over and along the guide wire to place the catheter within the patient with its distal end extending into the bile duct. The prosthesis, which fits slidably over the placed catheter then is advanced over the catheter and a pusher tube, which also fits slidably over the guiding catheter, is used to push the prosthesis through the patient along the catheter to a position within the bile duct. After the prosthesis has been placed the catheter, pusher tube and guide wire may be removed.
The procedure is traumatic to the liver and can be quite painful for the patient, particularly because of the enlarged diameter at the flared proximal end of the prosthesis. The flared proximal end, however, is essential if the prosthesis is to remain properly in place within the bile duct. In the absence of an enlargement on the prosthesis, such as the flared proximal end, natural peristaltic action would tend to advance the prosthesis out of the duct.
Another system is described by Kerlan et al, Biliary Endoprostheses, Radiology March 1984 pages 828-830. Kerlan describes the use of a technique in which a prosthetic tube is pushed from its trailing end while being pulled from its leading end. The technique uses a prosthetic tube having Mallecot tips formed at each of its ends. Mallecot tips are formed by a plurality of parallel longitudinal slits about the periphery of the tubular prosthetic to produce radially protruding lobes which can be heat set in a protruding or flowered position. Once the stent is positioned in the bile duct the flowered Mallecots prevent the peristaltic motion of the diatal bile duct from pulling the stent into the duodenum.
In the Kerlan procedure a guide wire is inserted percutaneously and transhepatically into and through the bile duct, duodenum, stomach, alimentary canal and out of the patient's mount. The stent is advanced into the patient by passing it over the guide wire at the mouth end and advancing it along the guide wire through alimentary canal, stomach, duodenum and into the bile duct. The stent is advanced by pulling it from its leading (hepatic) end while pushing it from its trailing (oral) end. In order to pull on the leading end of the stent a balloon catheter is passed over the guide wire from the percutaneously inserted end until the balloon tip is advanced to the patient's mouth. The balloon tip of the balloon catheter is inserted into the leading end of the stent and is positioned within the Mallecot tip. When the balloon is inflated it expands the Mallecot tip and becomes locked to it. The balloon catheter then may be withdrawn along the guide wire thereby pulling the stent by its leading end along the guide wire through the alimentary canal and toward the bile duct. Simultaneously a pusher tube is placed over the oral end of the guide wire and is used to push the stent from its trailing end. After the stent is positioned, the balloon catheter, pusher tube and guide wire are removed and the Mallecot's tips will remain in their expanded, flowered configuration to prevent migration of the stent from the biliary duct.
The technique described by Kerlan presents the same difficulty described above in connection with the Mendez technique in that the procedure results in an enlarged radial protrusion, in the form of the expanded Mallecot tip at each of the leading ends and trailing end. Thus, the technique described by Kerlan requires that the stent be forced through various passages while the Mallecot tips are in a flowered, enlarged configuration which makes it difficult and painful to advance and properly position the stent in the constricted bile duct.
The difficulties resulting from attempts to place a stent having flared or enlarged portion have been recognized. Koons et al, Large Bore, Long Biliary Endoprostheses (biliary stents) For Improved Drainage, Radiology July 1983 89-94 describes another technique in which the tubular stent does not have flared portions, Mallecot tips or other radial projections. Koons describes problems resulting from peristaltic migration of the stents and suggests that the problem might by overcome by using longer stents. However, even with a longer stent, there still remains a risk that the stent might be peristaltically advanced and discharged from the biliary duct.
It is among the general objects of the invention to provide an improved method and apparatus for placing a tubular stent which avoids the foregoing and other problems.